Just use the (hilarious) cop-out that archeologists always seem to adopt when they dig up some funerary site loaded with enough weed to keep the shaman or whoever buried there blasted out of his skull for most of eternity: “Oh, we suspect that the psychoactive plants buried with the shaman must have had a ritual purpose in the religious practices of X culture…”
‘Hey, man, I need a dimebag of ‘communion with the ancestor spirits’, if you know what I mean…’
